Those skilled in the hydrocarbon recovery operations have long recognized that plugback operations can enhance the recovery of oil and gas from wells. A water channel in a downhole formation may migrate over time to the wellbore, so that the water content of the fluids recovered at the surface becomes too high. A portion of the well above and below the water channel entry to the wellbore may thus be plugged in a workover operation, and hydrocarbons thereafter may again be economically recovered by perforating another zone. Wellbore plugback operations are also used for zone isolation purposes. Plugback operations are typically performed by utilizing a downhole setting tool to first set a bridge plug, then utilizing a dump bailer to release the bridging material, such as cement, onto the bridge plug.
U.S. Pat. No. 2,161,557 discloses an early type of wellbore fluid sampler including a biased valve which may be activated in response to a downhole clock. The sampling assembly includes batteries within the tool which allow movement of sampler components during a sequencing operation, after which the tool and sampled fluid are retrieved to the surface. U.S. Pat. No. 3,105,549 discloses a downhole tool containing an explosive charge which may be activated by a permanent magnet selectively positioned within the downhole tubular string. U.S. Pat. No. 3,105,550 discloses a magnetically activated well tool which may be suspended in the wellbore from a wireline. The tool may be used to introduce an inhibitrator fluid into the well, to perforate the tubing, or to set well completion or flow control equipment.
U.S. Pat. No. 3,373,817 discloses a technique for selectively releasing a cable-suspended tool. The releasing tool may be activated either in response to tension transmitted through the cable to the tool, or in response to an electrical signal transmitted from the surface through the cable to the tool. U.S. Pat. No. 3,665,955 discloses a control valve system for terminating the flow of oil and gas during a well blowout. The system includes downhole batteries which power an electric motor and drive gear assembly to close a ball valve. U.S. Pat. No. 4,796,708 discloses a safety valve for a well which is responsive to electromatic waves transmitted from the surface to the tool for opening and closing the valve. The downhole assembly includes an electric motor actuated by downhole batteries, with the motor and actuator being operable to open and close the safety valve. U.S. Pat. No. 5,188,172 discloses a downhole control valve assembly including a battery and a clock. The system also includes pressure and temperature sensors which may be placed in the wellbore above and below the valve for taking wellbore measurements.
Three types of tools are in common use today for performing plugback operations, and each type has significant disadvantages which have limited their use in the hydrocarbon recovery industry. The efficient recovery of hydrocarbons from the depleted wells and from wells having significant water intrusion has thus long demanded a reliable yet low cost technique for performing a plugback operation to plug in or close off a portion of a wellbore.
One type of well plugback tool utilizes a jarring action to mechanically activate or set a bridge plug, and subsequently utilizes a similar jarring action to release the plugging material from the dump bailer. The work string may thus be moved axially up and down to create the jarring action which is intended to activate the setting tool and the bailer. This jarring action may also be performed on a wireline suspended tool by jerking up on the wireline, and by releasing the wireline to land the tool on a hard bottom member. These jarring action techniques have generally proven to be unreliable, and thus are disfavored for most plugback operations by experienced hydrocarbon recovery operators. Downhole tools which rely upon a jarring motion for actuation often need a member within the wellbore to serve as a hard bottom, so that the jarring tool may strike this hard bottom to perform the desired jarring action. Additional time and expense are inherently required to position such a hard bottom in a wellbore at the desired location.
A second type of tool utilized in plugback operations activates the bridge plug and the dump bailer in response to an explosive charge. The bridge plug may thus be lowered to a selected depth from a wireline, and a blasting cap electronically activated to cause the setting of the bridge plug. The dump bailer similarly may thereafter be lowered to a location slightly above the set bridge plug, and the cement in the bailer released or dumped in response to the explosive force of a blasting cap, which may shear a pin to allow for axial movement of a mandril. Blasting caps and other explosive devices used in downhole operations are inherently considered hazardous, and accordingly should be used only by experienced personnel who have been specially qualified for these operations. The high cost of the regulations involving the transportation and use of such explosive equipment, and the risks inherently associated with these explosive devices, have thus severally limited the use of this technology for performing plugback operations.
A third type of tool utilizes a wireline to transmit an operating or activating current from the surface to the downhole setting tool and, subsequently, to the downhole bailer. The electrically transmitted operating current may activate a valve to release trapped fluid within the tool, thereby allowing a spring to activate the tool and either set the bridge plug, or release the bridging material from the dump bailer. Wireline setting operations are generally considered safe and reliable, although conductive wireline operations are also expensive. In some cases, plugback operations can be economically performed utilizing an electric wireline extending from the surface to the tool, particularly when a wireline logging tool has already been used to determine the water channeling point to the wellbore, and is thus at the well site. In many other cases, however, a wireline tool is not required to determine the water channeling point. Most conductive wireline service companies require their personnel on site during an electric wireline plugback operation, thereby significantly increasing costs. Accordingly, the widespread use of plugback operations has been limited, particularly in those instances where conductive wireline equipment and personnel are not otherwise required at the well site during the plugback operation. Many low or medium capacity hydrocarbon production wells are not being efficiently operated because of the unreliability, risks, or high costs associated with the plugback operation.
The disadvantages of the prior art are overcome by the present invention, and improved tools and techniques are hereinafter disclosed while performing a plugback operation. More particularly, the present invention discloses the reliable, safe, and comparatively inexpensive technique for reliably setting a bridge plug and/or releasing a bridging material from a dump bailer.